Wireless communications networks often use a control channel to communicate control information (e.g., resource allocation, modulation, and coding information, etc.) pertaining to a data channel. For instance, third generation partnership project (3GPP) Long Term Evolution (LTE) release 10 (rel-10) specifies communicating control information of a Physical Downlink Shared Channel (PDSCH) using a Physical Downlink Control Channel (PDCCH). The PDCCH is located in the control region of the sub-frame (which spans the first few leading symbols of the subframe), while the PDSCH is located in the data region of the subframe (which spans the remaining/trailing symbols of the subframe). Other control channels may also occupy the control region of the subframe. For instance, the control channel may include a Physical Hybrid Indicator Channel (PHICH) for carrying acknowledgment (ACK) and negative-acknowledgment (NACK) messages in response to uplink data transmissions and a Physical Control Format Indicator Channel (PCFICH) for indicating the number of symbols of control region in a subframe.
One proposed modification for future releases of LTE (e.g., 3GPP LTE-A release 11 (rel-11), etc.) is the introduction of an enhanced PDCCH (E-PDCCH) in the downlink subframe. The E-PDCCH may be used to carry uplink (UL) and/or downlink (DL) control signaling regarding the PDSCH and/or the physical uplink shared channel (PUSCH) to user equipments (UEs). Unlike previous control channels, the E-PDCCH will be located (at least partially) in the data region of the subframe, and may be frequency division multiplexed (FDM) with the PDSCH.
There may be multiple E-PDCCHs to communicate multiple control messages in a single PRB pair using time-division-multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, spatial division multiplexing (SDM) techniques, or combinations thereof. This ability to communicate multiple resource allocations in a single RB is particularly beneficial when high order modulation techniques are used, e.g., 16 quadrature amplitude modulation (QAM), etc. When an RB (or RB-pair) carries multiple control messages using TDM or FDM techniques, it is necessary to partition the RB (or RB-pair) by mapping available REs to multiple control channel elements (CCE). In this disclosure, CCEs of the E-PDDCH may be referred to as enhanced CCEs (eCCEs). For instance, an RB or RB-pair may be partitioned between a first eCCE (eCCE0) and a second eCCE (eCCE1).
It is desirable to evenly partition an RB (or RB pair) amongst the multiple eCCEs such that each eCCE is assigned/allocated the same number of REs. However, evenly partitioning an RB amongst multiple eCCEs is complicated by the existence of overhead information (e.g., reference signals, etc.) within the RB or RB pair carrying the E-PDCCH, which may be used for, inter alia, channel estimation (e.g., fading, etc.). Notably, the number and position of the overhead REs in the RB or RB pair varies depending on the configuration of the downlink channel, which means that an even partitioning of the RB or RB-pair cannot generally be achieved through a simple bifurcation of the RB or RB pair (e.g., splitting the RB in half along the time domain or frequency domain). That is to say, the sporadic and uneven interspersion of overhead REs within the RB or RB pair carrying the E-PDCCH would, more often than not, cause one of the halves to carry more overhead (and therefore fewer available REs) than the other. As such, a mechanism or technique for evenly partitioning the E-PDCCH between two or more resource allocations is desired.